GRB

Peter MészárosPennsylvania State University

Prompt and High Energy Emission

Mészáros

XO

R

Internal Shock

Fireball Model of GRBs

External Shock

Collisions betw. diff. parts of the flow

The Flow decelerating into the surrounding medium

GRBAfterglow

Mészáros

Prompt Optical Flashes : 3 models

• GRB 990123 → bright (9th mag) prompt opt. transient (Akerlof etal 99) . – 1st 10 min: decay steeper than forw.sh.• →Interpreted as reverse external shock

­

νFν

ν

Sy (rev)

Sy (forw)

0pt γ

Ext.Sh.

(1994-1997)

Mészáros & Rees ’97

Mészáros

9mag! (z=1.6)GR

B

Optical Flash : GRB 990123

ROTSE

(Akerlof et al. 1999; Meszaros & Rees 1997; Sari & Piran 1999; Kobayashi 2000)

Different time dep. of γ, opt. l.c. :→ infer opt is reverse shock

Mészáros

But: other prompt γ,opt ?

(Vestrand et al, 06)Sometimes same origin, sometime not ?

Mészáros

GRB080319B

Racusin et al, 2008 Nature

455:183

Interpret prompt as:i) optical synchrotron ii) 0.1-1 MeV IC (SSC)

(and)iii) predict 2nd order

IC @ ~100 GeV

“naked eye” optical GRB

z=0.937

γ,opt l.c. similar→same emiss. region,

but mechanism?

Mészáros

080319b

GRB 080318B

Opt

XR

Mészáros

080319B XR 2 jet fit

FS-NJ

FS-WJ

Mészáros

080319B opt. 2 jet fitRS-WJ

FS-WJ

Mészáros

GRB 080319B

WJ

NJ

GRB060218/SN2006aj –initial explosion

An unusually long, smooth burst, T90~2100±100 s

Low luminosity, low energy : Eiso~6x1049 erg

z=0.033, second nearest GRB (138 Mpc)

Campana et al. 2006

Subsequent evolution—SN emerges

Mazzali et al.2006Campana et al, 06, Nat 442:1008 Pian et al, 2006

A closer look at the XRT spectrum

Contribution of a fitted black-body component to the 0.3-10KeV flux

kT~0.17keV

Constitute 20% of the total XRT fluence

BB comp. temp. & radius

Mészáros

(1) BB XR Component: GRB060218/SN2006aj

• BB Interpreted as break-out of an anisotropic, semi-relativistic, radiation-mediated shock from opt. thick stellar wind (Campana et al 06, Nat. 442:1006; Waxman, Mészáros & Campana, astro-ph/0702450 -ApJ in press)

• Anisotropy is a crucial ingredient: timescale ~103 s is attributed to sideways pattern expansion speed, not to radial speed.

• Breakout when τT~c/vs, ocurring (in the wind) at Rph ~ 7x1012 (T/0.17 keV)-4/7 (Eth/1049 erg)3/7 cm, for mass loss dM/dt >10-4 Msun/yr when vw ~103 km/s

• Note : corresponds to mass loss within last day before explosion- no data on such winds

• Anisotropy of semi-relat. shell & wind compatible with & expected from rotation effects (e.g. Burrows et al, aph/0608033, Metzger et al, aph0608682, Burrows et al, aph/0702539, etc

14

060218 : non-thermal XR

Wang, Li, Waxman, Meszaros aph/0608033

Origin of non-termal gamma, X-rays:

Bulk comptonizationof semi-relativ. shock

thermal photons scattering against progenitor wind

(i.e., do not need highly relativistic jet

in low lum GRB/SN)

Other supernova-GRBs

1) Low-luminosity GRB (& often high luminosity SN..) 2) Smooth light curves 3) Spectrum: a simple power-law with a high energy cutoff Shorter T_90 duration for GRB980425 and GRB031203: possibly

shock breakout from the star envelope (i.e. no optically thick wind)

Mészáros

GRB prompt broadband emission

(CGRO era)

• Internal shock standard leptonic emission (sy, IC)

• Details depend on γe,min=εe(mp/me)Γsh

and εB (i.e. Compton Y)

• γγ cutoff @ GeV depends on tvar ( i.e.

rsh~ctvar Γ2 )Papathanassiou, PM 96

logεB=-3

logεB=0

GRB GeV emission: hadronic ?

pγ EM cascades

Boettcher & Dermer 98 ApJ 499, L131 ;Dermer, Atoyan 03, PRL 91, 1102;Dermer, Atoyan 04, AA418, L5

But:

• Ext. forw. shock synchrotron → MeV γs

• Proton acceleration (Fermi), spectral index -2, Up ~Ue,

⇒ p-synchr. & pγ cascades, → e+ sync, π0 dec.• Time decay of cascade radn, slower

than afterglow decay (p’s have less rad. losses) → distinguish from leptonic, detect with GLAST

Mészáros

GRB:prompt

GeV

Slow-coolhadronic

Eiso=1056 erg!

Slow-coolleptonic

Eiso=1053 erg

Gupta-Zhang 07 MN 380:78

Spectrum depends on whether leptonic or

hadronic;if e, cooling regime;

also B, Γ, r, etc.(semi-analytical)

basic int. shock model :

Mészáros

GRB prompt (lepto) GeV

Galli, Guetta 08arXiv:0709.4568

Broadbandspectra

simple SSC

Mészáros

XR Flares ⇒ GeV γ Flares?

21

Central engine

X-ray flare photons

Forward shock

XR flares ubiquitous in Swift XR ; thought to be late internal shocks (or mag diss) If so, → XR emission is inside the external shock→ IC upscatter XR photons by ext shock e- → GeV flares → GLAST det

X.Y. Wang, Li, Mészáros 06 ApJ 641:L89

Mészáros

XR → GeV Flares

22X.Y. Wang, Li, Mészáros 06 ApJ 641:L89(c.f. Galli, Piro et al 06: same shock self-SSC)

Swift

GLAST

Swift

int sy- int ICext sy-ext IC

int. sy-ext IC

Delay caused byanisotropic IC from higher lat.

Mészáros

Prompt hadronic

secondaryphotons

Asano & Inoue 07 ApJ 671:645Monte Carlo simulations:

Photon signature of protons may be easier to find than neutrinos!

Mészáros

Prompt hadronic secondary

photons (GeV)

Asano, Inoue & Mészáros arXiv:0807.0951

If GRB are UHECR sources, may need εp/εe ≳10 → tends to give

photon peak at higher energies

Diagnostic for↑: high εp/εp

←: high bulk Γ→ : high εB/εe

Mészáros

Conclusions• Will learn much from coordinated sub-MeV / GeV obs.• GRB 0980916c is the first high quality GeV GRB... now

need find others with simultaneous Swift/ground obs.• Will be able to constrain electron and proton

acceleration / shock parameters, compactness of emission region (dimension, magnetic field,...)

• Will constrain total energetics & fraction in UHECR, UHENU components

• Do GRB contribute significantly to UHECR? At what E?• Geometry of jet(s): progenitor & total GRB spatial

density needs will be better understood / constrained• Are there VHE-bright, MeV-dark GRBs? Relation to un-

ID TeV?